1. Field of the Invention
The present invention relates to a process cartridge mountable/demountable to an image forming apparatus such as an electrophotographic image forming apparatus.
The image forming apparatus refers to an apparatus for forming an image on a recording material by employing an electrophotographic image forming process. Examples of the image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (e.g., a laser beam printer, a light emitting diode (LED) printer), a facsimile machine, a word processor.
Further, the process cartridge is configured by integrally assembling into a cartridge a photosensitive drum as an image bearing member, and a developing roller (i.e., developer bearing member) as an image forming process unit acting on the photosensitive drum. Then, the process cartridge is configured to be detachably mountable to an apparatus main body of the image forming apparatus.
Further, the apparatus main body of the image forming apparatus refers to an image forming apparatus main body portion excluding the process cartridge.
2. Description of the Related Art
Conventionally, in an image forming apparatus using an electrophotographic image forming process, a photosensitive drum and an image forming process unit acting on the photosensitive drum are integrally assembled into a cartridge. Then, a process cartridge type in which the cartridge is mountable/demountable to the image forming apparatus main body is widely employed.
With the process cartridge type, a user can perform maintenance of the image forming apparatus without relying on a service engineer, and therefore operability can be dramatically improved.
For this reason, the process cartridge type is widely used in the image forming apparatuses.
The process cartridge is divided into a photosensitive drum unit having a photosensitive drum, and a developing unit having a developing roller. Further, the developing unit is configured to be relatively movable with respect to the photosensitive drum unit.
As one of the electrophotographic development types, there is a contact development type in which an elastic layer of the developing roller is contacted to the surface of the photosensitive drum to carryout image formation. In this case, the developing roller needs to be brought into contact with the photosensitive drum uniformly in a rotational axis direction of the photosensitive drum.
The developing roller is used by being urged to maintain a predetermined position at which the developing roller acts on the photosensitive drum at the time of image formation. As one of methods for urging the developing roller at a predetermined position, there is a type for supporting swingably with respect to the photosensitive drum, at both ends in a rotational axis direction of the developing roller of the developing unit, and swinging the developing unit by an urging member for applying a moment in a direction in which the developing roller comes into contact with the photosensitive drum.
The both ends in the rotational axis direction of the developing roller of the developing unit are supported swingably with respect to the photosensitive drum. In that case, the alignment between the rotational shaft of the developing roller, and a swing shaft of the developing unit is deviated due to component tolerance or the like. For this reason, a contact pressure of the developing roller with respect to the photosensitive drum may become non-uniform.
For example, Japanese patent Application Laid-Open No. 9-50224 discusses a configuration in which one end side in a rotational axis direction of the developing roller is supported swingably with respect to the photosensitive drum unit, and the other end side is supported swingably and movably. With this configuration, deviation of the alignment between the rotational shaft of the developing roller and the swing shaft of the developing unit is permitted.
However, in Japanese patent Application Laid-Open No. 9-50224, the other end side in the rotational axis direction of the developing roller of the developing unit is supported swingably and movably with respect to the photosensitive drum. Accordingly, the other end side in the rotational axis direction of the developing roller of the developing unit has a predetermined degree of freedom, and positioning is not performed positively.
Consequently, there is a problem that the contact position of the developing roller and the surface of the photosensitive drum may vary. As a result, the contact pressure of the developing roller to the photosensitive drum becomes unstable.
Conventionally, by optimizing an arrangement among the rotation center of the developing roller, the rotation center of the photosensitive drum, and the swing center of the developing unit, stabilization of the contact position of the developing roller and the surface of the photosensitive drum has been achieved.
For example, as illustrated in FIG. 11, an angle θ2 formed by a straight line “U” connecting a swing center “X” of the developing unit 9 and a contact point “N” of the developing roller 6 and the photosensitive drum 4, and a straight line “W” connecting a rotational shaft 6b of the developing roller 6 and a rotational shaft 4b of the photosensitive drum 4 is set at substantially right angle. Then, the contact position of the developing roller 6 and the surface of the photosensitive drum 4 becomes stable. Then, the contact pressure of the developing roller 6 to the photosensitive drum 4 becomes stable.
On the other side, in order to downsize the process cartridge P, a degree of freedom needs to be increased to the arrangement of each of the rotational shaft 6b of the developing roller 6, the rotational shaft 4b of the photosensitive drum 4, and the swing center “X” of the developing unit 9. Consequently, the angle θ2 at which the contact position of the developing roller 6 and the surface of the photosensitive drum 4 becomes stable may not be set at substantially right angle. As a result, the contact position of the developing roller 6 and the surface of the photosensitive drum 4 may vary, and the contact pressure of the developing roller 6 to the photosensitive drum 4 may become unstable.